Marked Reduction in the Number of Platelet—Tritiated Imipramine Binding Sites in Geriatric Depression

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Abstract
• The number (Bmax) and affinity (Kd) of platelet—tritiated imipramine binding sites was determined in young and middleaged controls 50 years of age and younger (n = 25), elderly normal controls over 60 years of age (n=18), patients who fulfilled DSM-III criteria for major depression who were under 50 years of age (n=29), patients who fulfilled DSM-III criteria for major depression who were 60 years of age and older (n=19), and patients who fulfilled both DSM-III criteria for primary degenerative dementia and National Institute of Neurological and Communicative Disorders and Stroke—Alzheimer's Disease and Related Disorders Association criteria for probable Alzheimer's disease (n =13). Both groups of depressed patients (under 50 and over 60 years of age) exhibited significant reductions (↓42%) in the number of platelet— tritiated imipramine binding sites with no change in affinity, when compared with their age-matched controls. There was little overlap in Bmax values between the elderly depressed patients and their controls. The patients with probable Alzheimer's disease showed no alteration in platelet—tritiated imipramine binding. There was no statistically significant relationship between postdexamethasone plasma cortisol concentrations and tritiated imipramine binding. These results indicate that platelet—tritiated imipramine binding may have potential utility as a diagnostic adjunct in geriatric depression, and moreover that the reduction in the number of platelet— tritiated imipramine binding sites is not due to hypercortisolemia.